JP2007531310A - Surface-mount multichannel optical coupling device - Google Patents

Abstract

  An optocoupler package is disclosed. The optical coupling element package includes a substrate including a lead frame and a molding compound, and a plurality of optical coupling elements. Each optical coupling element includes (i) a light emitting element, (ii) a light receiving element, and (iii) a light receiving element and a light receiving element. The light-emitting element and the light-receiving element are electrically coupled to the lead frame, including a light-transmitting medium placed between the elements.

Description

(Background of the Invention)
The optical coupling element includes at least one light emitting element that is optically coupled to the light receiving element through the light transmissive medium. With this arrangement, information can be transferred from one electric circuit including the light emitting element to another electric circuit including the light receiving element. A high degree of electrical isolation is maintained between the two circuits. Since information is optically passed across the insulation gap, transmission is one way. For example, the light receiving element cannot change the operation of a circuit including the light emitting element. This feature is important. For example, the light emitting element may be driven by a low voltage circuit using a microprocessor or logic gate, while the output light receiving element may be part of a high voltage DC or AC load circuit. Optical isolation also prevents damage to the input circuit caused by relatively conflicting output circuits.

  A common optocoupler package format is the dual in-line package or DIP. This package is widely used to accommodate integrated circuits and is also used for conventional optocouplers. Various types of optocoupler DIP packages with 4, 6, 8 or 16 pins are generally manufactured.

  FIG. 1 shows a cross-sectional view of a conventional optical coupling element DIP package 10. The illustrated optical coupling element 10 includes a lead frame 24 including leads 24 (a), 24 (b) (ie, pins). The light emitting element 12 is mounted on one lead 24 (a). The light receiving element 14 is mounted on another lead 24 (b). The light receiving element 14 receives the light generated by the light emitting element 12 and then generates an electrical signal. The light emitting element 12 is electrically coupled to the lead 24 (a) through the bottom surface thereof, and is coupled to another lead (not shown) via the wire 11. Similarly, the light receiving element 14 is electrically coupled to the lead 24 (b) through the bottom surface and is coupled to another lead (not shown) via the wire 13. Those skilled in the art will appreciate that the light emitting device 12 operates with two electrical connections, one anode and one cathode. These connections are thus provided by wire 11 and lead 24 (a). Similarly, the light receiving element 14 operates with two electrical connections, usually an emitter and a collector. These connections are provided by wires 13 and leads 24 (b). The optocoupler package 10 further includes a light transmissive medium 16. The molding compound 18 encloses the lead frame 24, the light emitting element 12, the light receiving element 14, and the light transmissive medium 16.

  Several improvements can be made to the optocoupler package 10 shown in FIG. For example, the optocoupler package 10 requires an expensive and time-consuming overmolding process. In the overmolding process, the molding compound 18 encapsulates other parts of the optical coupling device package 10. In addition to the overmolding process itself, a molding material removal process (eg, dejunk and deflash process) is used to remove excess molding compound, thus increasing the time and cost of forming the optocoupler package. ing. In addition, the production equipment needed to create different “form factors” (eg, a package of 4, 6 or 8 pins) requires significant capital investment. Therefore, if the overmolding process can be omitted, the time and cost involved in manufacturing the optical coupling device package can be reduced.

  Other improvements to the optocoupler package 10 can also be made. Optocoupler package 10 is also prone to failure from thermal cycling. For example, differences in the thermal expansion properties of the molding compound 18 and the light transmissive medium 16 cause them to expand and contract at different rates when they are heated or cooled. Molding compound 18 and light transmissive medium 16 may separate, resulting in a structurally weak package. The temperature cycle also generates stress at the point where the lead frame 24 exits the molding compound 18 (eg, at the “A” point). As a result, the lead frame 24 may be broken or weakened due to the stress. Also, the wires 11, 13 sometimes pass through the light transmissive medium 16 and the molding compound 18. Differences in the thermal expansion properties of the light transmissive medium 16 and the molding compound 18 can induce stresses in the wires 11, 13 that can break them.

  It is also desirable to reduce the height of the conventional optocoupler package. The optocoupler package 10 shown in FIG. 1 is relatively high. For example, the net height of a typical DIP package is about 3.5 to about 4.0 mm. It is desirable to reduce the height of the optocoupler package so that it has a lower profile. By doing so, smaller electronic components can be manufactured.

  It would also be desirable to increase the functionality of the package and reduce the costs associated with manufacturing optocoupler packages.

  Embodiments of the present invention address these and other issues individually and collectively.

(Summary of the Invention)
Embodiments of the present invention relate to an optical coupling element package and a method for producing the same.

  One embodiment of the present invention includes (a) a substrate including a lead frame and a molding compound, (b) a light emitting element, (c) a light receiving element, wherein the light emitting element and the light receiving element are electrically coupled to the lead frame; And (d) a light coupling element package including a light transmitting medium placed between the light emitting element and the light receiving element.

  Other embodiments of the present invention include: (a) forming a substrate including a lead frame and a molding compound; (b) attaching a light emitting element and a light receiving element to the substrate; and (c) a light emitting element and a light receiving element. The present invention relates to a method for forming an optical coupling element package, comprising attaching a light transmissive material therebetween.

  Other embodiments of the present invention include: (a) a substrate; (b) at least two light emitting elements; (c) at least two light receiving elements; and (d) light transmission between adjacent light emitting elements and light receiving elements. A light coupling element package, wherein the light emitting element and the light receiving element are on a substrate.

  These and other embodiments are described in more detail below.

(Detailed explanation)
In an embodiment of the invention, the one or more optical coupling elements are on a single substrate formed from a lead frame and a molding compound. For example, there may be four optocouplers in four arrays on a single substrate. Each optical coupling element can include a light emitting element (eg, a light emitting diode) and a light receiving element (eg, a photodiode). The spacing between the light receiving element and the light emitting element can be from about 0.3 mm to about 0.5 mm. Each light coupling element can be fixed with a light transmissive bonding gel and encapsulated with an opaque, highly reflective epoxy-based polymer. The functional terminals for the optocouplers can be grouped and routed towards the periphery of the package so that a ball grid array arrangement is formed. The light receiving element, the light emitting element, and the wire bond pad are arranged so as to correspond to the terminals of the lead frame.

  Logic elements, such as control chips, can be on a lead frame based substrate or in an optocoupler package. A chip including a MOSFET (metal oxide semiconductor field effect transistor) such as a power MOSFET with or without a trench gate may be on a substrate or in a package. Such a chip or element may be on a substrate and may be electrically coupled to components such as a light emitting element and a light receiving element.

  In some embodiments, the optocoupler package is thin and has at least two optocouplers (eg, four optocouplers). As an advantage, a single optocoupler package can provide comparable or better performance compared to four stand-alone optocoupler packages, each having one optocoupler. As shown below, the peripheral solder ball placement in the package allows for a simpler board design. This is because the routing of the conductive traces has already been incorporated into the optocoupler package. This also saves space on the substrate where the optocoupler package is mounted.

  2 and 3 show the lead frame substrate 1 before molding used in the optical coupling element package. This substrate includes a lead frame 2 and a molding compound 3. The lead frame 2 may include a die attachment region in which two or more dies including a light receiving element and a light emitting element are placed. Additional chips, such as control chips, can also be mounted on the lead frame. Two or more leads may extend from the die attach area and may form the terminals of the lead frame. A “lead frame” includes a lead frame structure that may or may not have been processed (eg, by etching). In other cases, other types of substrates may be used.

  4 and 5, the lead frame 2 is a skeleton framework of the substrate 1. This is to define functional pads and fixed areas (for fixing the molding compound 3) of the substrate 1, in which a complex half-etched 2a, an unetched 2b, and a through-hole or It has a fully etched 2c pattern.

  The lead frame 2 can include any suitable metal and can be any suitable thickness. For example, a copper alloy with high mechanical strength is desirable. The lead frame 2 can have a thickness of about 0.2 mm (8 mils) or less in the etched or unetched areas. Etching processes are well known to those skilled in the art. The lead frame 2 may also include a gold plating layer such as Ni, Pd, Au, or Ag.

  The molding compound 3 of the substrate 1 forms the body of the substrate 1. This fills the through hole 2c and the half-etched region 2a of the lead frame 1. In this example, the unetched region 2 b of the substrate 1 is not covered with the molding compound 3.

  The molding compound 3 can include polymeric materials and / or composite materials, which may or may not require post-mold curing. Molding compounds may include epoxy resins, curing agents, elastomers, non-phosphorous flame retardants, lubricating oils, silicic acid fillers, and others. The molding compound may balance the size of the molecules therein to ensure complete filling of the half-etched areas of the lead frame 2. The molding compound may also contain a sufficient amount of carbon black pigment for better laser marking contrast. Materials that make up the balance of the molding compound 3 composition material can be used to prevent distortion of the substrate.

  In some embodiments, the substrate 1 can be formed using tape. For example, the tape can be attached to the unetched pad 2 b of the lead frame 2 so that the molding compound 3 (or molding bleed or molding bite) does not occupy the functional pads of the substrate 1. The non-tapeed side of the lead frame 2 is overmolded by about 0.1 mm to add mechanical strength to the substrate 1. In other embodiments, there is no overmolding and the molding compound 3 is only in the gap of the lead frame 2. The thickness of the substrate 1 can vary depending on the mechanical and physical requirements of the package 20.

  As shown in the drawing, the molding compound 3 on the substrate 1 defines a functional pad. These functional pads are unetched regions 2b of the lead frame 2.

  Details of additional substrate formation are disclosed in US patent application Ser. No. 10 / 233,248, filed Aug. 30, 2002, which is hereby incorporated by reference in its entirety.

  Referring to FIG. 6, the optical coupling element package may be divided into four quadrants having four optical coupling elements, optical coupling elements I-IV. The optical coupling element I occupies the quadrant I (101). The optical coupling element II occupies the quadrant II (102). The optical coupling element III occupies the quadrant III (103). The optical coupling element IV occupies a quadrant IV (104).

Referring to both FIGS. 6-7, the functional pads of the substrate 1 can be classified as follows.
(A) The four internal assembly pads of optocoupler I21 are cathode I (or diode die attach pad I) 4a, anode I (or diode weld pad I) 5a, collector I (or phototransistor die attach pad). I) 6a, and emitter I (or phototransistor welding pad I) 7a.
(B) Four internal assembly pads of optocoupler II22 are cathode II (or diode die attach pad I) 4b, anode II (or diode weld pad II) 5b, collector II (or phototransistor die attach pad). II) 6b, and emitter II (or phototransistor welding pad II) 7b.
(C) The four internal assembly pads of optocoupler III23 are cathode III4c, anode III5c, collector III6c, and emitter III7c. And
(D) The four internal assembly pads of optocoupler IV24 are cathode IV4d, anode IV5d, collector IV6d, and emitter IV7d.

The unetched functional pads of the substrate 1 are connected to terminal pads for peripheral solder ball attachment. These are grouped and routed to create a symmetric package substrate 1 with common terminal pads. The peripheral ball mounting pads are classified as follows.
(E) The cathode or diode die attach pads (4a, 4d) of optocouplers I and IV are shorted, connected to common cathode terminal pad 8a, and placed on the outer edges of quadrants I and IV. .
(F) The cathode or diode die attach weld pads (4b, 4c) of optocouplers II and III are short-circuited, connected to the common cathode terminal pad 8b, and placed on the outer edges of quadrants II and III Yes.
(G) Each of the anode terminal pads 9a, 9b, 9c, 9d of all the optical coupling elements is independently placed at a corner around each quadrant.
(H) The collector terminal pads 10a, 10b, 10c, and 10d of each optical coupling element are independently placed laterally on the opposite side of the anode terminal pad.
(I) The emitters or phototransistor welding pads 7a, 7b, 7c, 7d of all optocouplers are shorted and routed towards the central horizontal periphery of the substrate, resulting in two Symmetric peripheral terminal pads 11 are formed. The anode-cathode pad maintains a gap of about 0.5 mm from the emitter-collector pad in all optocouplers. This ensures a high voltage breakdown for each optocoupler.

  FIG. 7 shows an optical coupling element package 20 including four optical coupling elements including domes 21, 22, 23 and 24 with rounded apexes. The rounded apex material does not contact the ball mounting peripheral terminal pads 8a-8b, 9a-9d, 10a-10d (shown in FIG. 6).

  The optical coupling element package 20 includes external peripheral solder balls 25 attached to the substrate 1. The peripheral ball 25 is attached to the terminal pads 8a-8b, 9a-9d, 10a-10d, and 11. These balls 25 function as a direct connection mechanism to the printed wiring board (PCB) 31 for the optical coupling element package 20 (see FIG. 11). It is desirable that the solder ball 25 contains an alloy having a high melting temperature and not containing Pb.

  As shown in FIG. 7, in the illustrated example, the optocoupler package 20 has twelve equally spaced peripheral solder balls 25. The configuration with peripheral balls outside the package may be modified (based on the same concept as internal assembly pad shorts and terminal routing) by the requirement and die to pin out of a particular package. Although solder balls are described in detail, other conductive structures such as copper pillars (eg, pre-formed or electroplated) can be used instead. The conductive structure has a height higher than the height of the light receiving element and the light emitting element in the optical package so that flip chip mounting can be performed.

  Referring to FIGS. 9 and 10, the LED die 26 generates photons when a forward current is applied to the optocoupler, resulting in light emission from the PN junction in the die 26. An LED die having a height of about 9 mils or less can be used.

  Phototransistor die 27 detects the light emitted by LED die 26 and converts it to electrons, resulting in a current at the optocoupler output. Light sensing occurs at the collector-base junction. Phototransistor dies as high as about 8 mils or less can be used.

  Referring to FIGS. 6, 9 and 10, a die attach material (not shown) bonds the back of each LED die 26 to its designated die attach pad 4a, 4b, 4c, 4d. Similarly, it bonds the back of each phototransistor die 27 to its designated die attach pad 6a, 6b, 6c, 6d. The die attach material can be any conductive adhesive. Examples include Ag-filled epoxy, soft solder, and others. In some embodiments, die attach bands can be used and can be controlled at up to about 50% of the die height to maximize light emission from the LED die 26 side.

  Bonding wire 28 connects the anode pad of LED die 26 to diode welding pads 5a, 5b, 5c, 5d, completing the circuitry of the diode components of package 20. They likewise connect the phototransistor die 27 to their designated welding pads 7a, 7b, 7c, 7d. Bonding wire 28 may include any suitable ductile metal—Au, Cu, Al, or doped variations of these metals, alloys of these metals, and the like. The wire loop is preferably about 14 mils from the substrate.

  The wire bond LED die and phototransistor die assembly are bonded using a light transmissive transparent gel material 29. The light transmissivity of the bonding gel 29 enables effective transfer of light emitted from the LED 26 junction toward the photosensitive junction of the phototransistor 27. Bonding gel 29 covers the entire wire bond die assembly and forms a generally hemispherical dome for maximum transmission of the emitted light.

  The light transmissive hemispherical dome 29 of each of the wire bond LED and phototransistor assemblies is covered with a white reflective apex round material 30 to complete one optocoupler internal package structure. The round apex 30 (or light reflective material) is a light reflective material that keeps the emitted light within the dome. The rounded apex coating conforms to the shape of the dome and can completely cover the transparent bonding gel 29 (or light transmissive material). This seals the dome by gluing. The rounded apex material 30 can have a minimum thickness of about 0.2 mm.

  The optical coupling element package can be manufactured by the following process.

  First, a lead frame molding process can be performed. As described above, the lead frame molding process is performed using a lead frame with a tape attached thereto. A piece of tape can be applied to the unetched pad of the lead frame so that the molding compound does not occupy the functional pads of the subsequently formed substrate. The non-tapeed side of the lead frame is overmolded to add mechanical strength to the substrate.

  Second, a die attach process can be performed. For example, LEDs and phototransistor dies can be attached using an adhesive with a conductive filler or solder. Die attach curing may or may not be necessary depending on the type of adhesive used.

  Third, a wire bond process can be performed to form a conductive path between the dies on the substrate and their corresponding pads. For example, in some embodiments, a thermosonic or ultrasonic wire bonding process can be performed.

  Fourth, a dome coat and cure process can be performed. Any suitable liquid dispensing process can be used to dispense the transparent binding gel to form a light transmissive hemispherical dome. Curing may be necessary to improve the physical properties of the bonded gel. Suitable dome coat materials include silicon-based materials available from Dow Corning and General Electric, but any suitable sales company may be used.

  Fifth, round vertices and curing processes can be performed. Any suitable liquid dispensing process can be used for the opaque rounded apex. Curing may or may not be necessary depending on the type of material used. Suitable reflective coating materials include epoxy based coatings having reflective pigments based on materials such as titanium dioxide or other metal oxides. These can be purchased from Epotek and Hysol, but any suitable sales company may be used.

  Sixth, a solder deposition process can be performed (eg, for solder ball 25 in the figure). Solder ball attachment, fluxing, ball placement or ball firing, ball injection, and other processes can be used to attach conductive structures such as solder to the substrate. In other examples, conductive columns (eg, copper columns) can be placed on the substrate instead, or can be electroplated on the substrate.

  Seventh, a solder reflow process can be performed (if solder is used). In some embodiments, a reflux or conduction or diffusion solder reflow process can be used.

  Eighth, individualization processing can be executed. Individualization processes include blade sawing, water jet sawing, laser sawing and others. In the individualization process, the formed substrates are separated from each other.

  Ninth, an electrical test can be performed. High pressure inspection and parametric inspection can be used to eliminate any packages with electrical defects.

  Tenth, a package marking process can be performed. Laser or pad marking or other processes can be used to provide package identification and orientation.

  Once the package is formed, it can be turned over and mounted on a printed wiring board as shown in FIG. Common surface assembly techniques can be used.

  It should be noted that the above processes can be performed in the above order, or can be performed in a different order.

  It should be noted that the present invention is not limited to the preferred embodiments described above. It will be apparent that changes and modifications by those skilled in the art may be made within the spirit and scope of the invention. Furthermore, any one or more embodiments of the present invention may be combined with one or more embodiments of the present invention without departing from the spirit and scope of the present invention.

  All US provisional and formal patent applications and publications mentioned above are hereby incorporated by reference in their entirety for all purposes. None of these are recognized as prior art.

It is a figure which shows the optical coupling element package of a prior art. FIG. 3 is a view from the bottom of a substrate according to one embodiment of the present invention. It is a figure which shows the internal lead frame structure of the board | substrate in FIG. FIG. 6 is a bottom plan view of the substrate shown in FIG. 5. FIG. 5 is a side sectional view taken along line AA of the substrate shown in FIG. 4. FIG. 10 is another bottom plan view of the substrate showing different optical coupling element quadrants. It is the figure seen from the bottom face of the optical coupling element package by one Example of this invention. It is the figure seen from the upper surface of the optical coupling element package by one Example of this invention. It is the bottom view seen from the bottom of an optical coupling element package, and the light emitting element and the light receiving element are shown. It is a bottom plan view of an optical coupling element package showing a light receiving element and a light emitting element. FIG. 3 is a diagram illustrating an optical coupling element assembly including an optical coupling element package mounted on a substrate.

Claims (20)

An optical coupling element package,
(A) a substrate including a lead frame and a molding compound;
(B) a light emitting element;
(C) the light receiving element, the light emitting element and the light receiving element are electrically coupled to the lead frame;
(D) a light-transmitting medium placed between the light-emitting element and the light-receiving element;
The optocoupler package comprising:   The optical coupling element package according to claim 1, further comprising a plurality of conductive structures coupled to the lead frame, wherein the conductive structure has a height higher than heights of the light receiving elements and the light emitting elements. The optocoupler package, comprising:   3. The optical coupling element package according to claim 2, wherein the conductive structure is a solder structure.   2. The optical coupling element package according to claim 1, further comprising a bond wire that electrically couples the light receiving element to the lead frame and electrically couples the light emitting element to the lead frame. The optical coupling element package.   2. The optocoupler package according to claim 1, wherein the lead frame includes an etched portion and an unetched portion, and the etched portion is covered with the molding compound and is not etched. Is not covered with the molding compound.   The optical coupling element package according to claim 1, wherein the lead frame includes copper.   2. The optical coupling element package according to claim 1, wherein a plurality of optical coupling elements are on the substrate.   6. The optocoupler package according to claim 1, wherein the lead frame includes an etched portion and an unetched portion on a first side, and the etched portion is covered with the molding compound and etched. The non-covered portion is not covered with the molding compound, and the molding compound completely covers the second side of the lead frame. A method of forming an optocoupler package comprising:
(A) forming a substrate including a lead frame and a molding compound;
(B) attaching a light emitting element and a light receiving element to the substrate;
(C) attaching a light transmissive material between the light emitting element and the light receiving element;
Said method. The method of claim 9, further comprising:
Forming a plurality of conductive structures on the substrate, wherein the conductive structures have a height higher than the height of the light emitting element and the light receiving element.   10. The method of claim 9, wherein the method includes etching the lead frame prior to (a).   The method of claim 9, wherein the lead frame comprises copper.   10. The method of claim 9, further comprising attaching a wire from the light emitting element and the light receiving element to the lead frame.   The method of claim 9, further comprising depositing an opaque material on the light transmissive material.   10. The method of claim 9, further comprising mounting at least four light emitting elements and at least four light receiving elements on the substrate. An optical coupling element package,
(A) a substrate;
(B) at least two light emitting elements;
(C) at least two light receiving elements;
(D) a light transmissive medium between adjacent light emitting elements and light receiving elements;
(E) a light reflective material on the light transmissive medium;
Including
The optical coupling element package, wherein the light emitting element and the light receiving element are on the substrate.   17. The optocoupler package according to claim 16, wherein the substrate includes a lead frame including an etched portion.   17. The optical coupling element package according to claim 16, wherein the substrate includes a lead frame including copper and a molding compound.   The optical coupling element package according to claim 16, further comprising a chip including a MOSFET on the substrate.   2. The optical coupling element package according to claim 1, further comprising a chip including a MOSFET on the substrate.

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